The present invention relates to semiconductor technology, and more particularly to a semiconductor device and manufacturing method thereof.
Integrated optical waveguide sensors have been developed based on integrated optics technology. Integrated optical waveguide sensors not only have the benefits of fiber optic sensors, but also offer the advantages of multi-functional integration capability, smaller size, lighter weight, higher reliability, lower power consumption over conventional sensors. Integrated optical waveguide sensors are an important part of the new generation of miniaturized, integrated and smart sensor systems.
When sensors become more sophisticated and more demanding in the degree of integration, the benefits of integrated optical waveguide sensors become increasingly more evident and the application areas become more extensive. Integrated optical waveguide sensors are currently used in sensing pressure, electromagnetic field, gas or liquid flow, acceleration, angular velocity, etc. Silicon dioxide as a material for sensing components of an optical waveguide cantilever beam has been extensively studied.
At present, isotropic dry etching is used to form an oxide cantilever beam. When the predetermined width of the oxide cantilever beam is significantly larger than the opening width of the semiconductor substrate, silicon residues are generally present below the oxide cantilever beam and prevent the suspension of the cantilever beam. In order to prevent transmission loss of light or optical signals, an organic polymer is filled below and above the cantilever beam, however, the form (morphology) of the cantilever beam after the isotropic dry etching generally hinders the filling of the organic polymer.
FIGS. 1A through 1E are simplified cross-sectional views illustrating stages of process steps of forming a semiconductor device according to the prior art.
Referring to FIG. 1A, a semiconductor substrate 100 is provided, a thermal oxide layer 101 and a HDP silicon oxide layer 102 are successively formed on semiconductor substrate 100. A patterned photoresist layer 103 is formed on HDP silicon oxide layer 102.
Referring to FIG. 1B, thermal oxide layer 101 and HDP silicon oxide layer 102 are etched using patterned photoresist layer 103 as a mask until a surface of semiconductor substrate 100 is exposed to form an opening 104.
Referring to FIG. 1C, semiconductor substrate 100 is isotropically etched to form a cantilever beam 105. When the predetermined width We of cantilever beam 105 is larger than the width Wo of opening 104, silicon residues 110 are generally present below cantilever beam 105 and in the worst case, make impossible the suspension of cantilever beam 105. An increase in the isotropic dry etching process time cannot solve this problem.
Referring to FIG. 1D, an organic polymer 106 is filled over semiconductor substrate 100 and cantilever beam 105, the poor morphology of cantilever beam 105 (due to the residue 110) may hinder the filling of organic polymer 106 in the space below cantilever beam 105. Thereafter, a patterned photoresist layer 107 is formed on organic polymer 106.
Referring to FIG. 1E, organic polymer 106 is etched using patterned photoresist layer 107 as a mask. The etching stops when a surface of HDP silicon oxide layer 102 is exposed.
As described above, the presence of silicon residues underneath the cantilever beam may hinder the filling of an organic polymer and make the suspension of the cantilever beam impossible, and an increase in isotropic dry etching time may not solve this problem. For these and other reasons there is a need for the present invention.